Sump level control for hydraulic classifier circuit



Sept. 21, 1965 A. YESBERGER SUMP LEVEL CONTROL FOR HYDRAULIC CLASSIFIER CIRCUIT Filed Sept. 25, 1962 I L we Wm m s 5 m K .Q a 2n mw av. LB L United States Patent 3,207,310 SUMP LEVEL CONTROL FOR HYDRAULIC CLASSIFIER CIRCUIT Lloyd A. Yesberger, Brecksville, Ohio, assignor to Republic Steel Corporation, Cleveland, Ohio, at corporation of New Jersey Filed Sept. 25, 1952, Ser. No. 226,114 5 Claims. (Cl. 209-155) The invention relates to means for controlling the sump level in a hydraulic classification circuit such as is used for example in the treatment or beneficiation of ores. In such classification it is desirable to control the classification circuit so that sizing variation will be held to a minimum, and this is especially true when the circuit includes separation means of the cyclone classifier type used in one successful commercial process for the beneficiation of comminuted taconite ore wherein the concentrated ferrous metal fraction is selectively separated from tailings.

As will appear more in detail hereinafter, and still using as an example the beneficiation of ground taconite ore, an ore slurry is fed to one or more successive stages of ball mill grinding and magnetic separation, the mesh size of the particles in the final slurry being approximately thirty percent minus 325 mesh. After the last stages of grinding and magnetic separation the pulp fraction is discharged into a sump whence it is pumped to a hydroseparator such as a cyclone classifier from which a coarser fraction is returned in closed circuit to the ball mill and a finer fraction is routed, for example, to further hydroseparators to further upgrade the beneficiated concentrate.

In the embodiment of my invention to be described herein the pulp is transferred from the sump to the cyclone classifier by means of a pump. The outlet pressure of the pump is controlled by the load, this term being a summation of several factors, including static head, line friction and pressure drop through the cyclone classifiers. When these factors are maintained at a constant value the system operates at maximum efliciency.

Still using as an example the beneficiation of taconite ore, it is desirable to produce a concentrate of controlled sizing so as to give the subsequent pelletizing operation the best possible raw material to produce the pellets. To achieve this aim it is necessary to maintain close control of the cyclone classification circuit so as to hold the sizing variation to a minimum. This requires a constant volume of pulp delivered at a uniform rate of flow, and at a constant pressure, to the cyclone classifiers.

To avoid cavitation in the pump the inflow to the sump must equal or exceed the capacity of the pump. To avoid overflow, and loss of pulp, the inflow to the sump should not normally be more than the capacity of the pump.

An object of the present invention is to devise means for controlling the level in the sump tank upstream from the pump whereby to provide a uniform stream of pulp to the cyclone classifiers.

A further object of the invention is to provide sump level control means at low initial cost and requiring practically no maintenance cost.

A further object of the invention is to provide sump level control means which eliminates cavitation in the pump and greatly increases the wear life of the pump arts. P A further object of the invention is to provide sump level control means which eliminates surging in the pump whereby to insure a uniform flow to the classifiers.

Other objects and advantages will be apparent from a study of the following description of one embodiment of the invention in conjunction with the accompanying draw- Patented Sept. 21, 1965 "ice The drawing shows, in schematic form, a pulp flow circuit embodying my sump level control system.

In the drawing there is shown a ball mill 20 which feeds a slurry of iron-rich ore and mostly silicious tailings (the slurry being herein termed pulp) to a magnetic separator 21 where a certain amount of non-magnetic fraction is removed, the balance entering a sump or tank 22 at 23. From the sump the pulp flows through pipe 24 to the intake side of pump 25 whence it is impelled through successive pipes 26 to the cyclone classifier 27. Classifiers of this general type are known in the art and need not be further described herein. Briefly, their function is to separate the pulp or concentrate slurry into a finer and a coarser portion, the finer portion going (route 28) to finishing separators or filters, and the coarser portion (route 29) being returned to the input of the grinding mill 20. The sump has an overflow weir level at the bottom edge 30 of a slot in the sump tank side wall. With the apparatus so far described if the pulp feed at 23 slows down or stops the sump level falls until the pump intake no longer has a satisfactory flow, and pump cavitation takes place.

By means of the apparatus now to be described I have succeeded in maintaining the pulp level at an optimum position. I provide a control tank 33 which has a Water intake 34 and an outlet 35, the outlet being in flow communication with the sump by means of a pipe 36 having aperture-restricting means such as a valve 37. The result can also be achieved by a proper length of pipe sized to produce the desired flow characteristics. Control tank 33 has a constant level determinable by an overflow outlet at 38. In simplest fashion this level can be maintained by introducing a continual water feed at 34.

As long as the water-level plane, indicated by the broken line 39, is higher than the pulp level in the sump, water willflow through pipe 36 into the sump to bring the sump level to approximately the broken line 40. As the level in the sump rises the differential pressure in pipe 36 decreases until equilibrium is attained between lines 39 and 40. Since the slurry or pulp in the sump contains entrained material of substantial iron content, equilibrium will be established at respectively separate planes, for example at 39 and 40, though the line 40 will vary depending on variations in ore content of the pulp. If the overflow level at 38 is high enough there will always be enough hydrostatic pressure in the control tank 33 to prevent sand or solids from flowing through pipe 36 into the control tank.

The control device disclosed hereinabove is relatively fool proof as long as the water feed at 34 is sufiicient to produce an overflow at 38. If for any reason the supply of pulp from the magnetic separator at 21 is substantially or completely cut off, the control tank 33 will maintain the level in sump 22 although of course the pump 25 will be pumping a low solid content liquid to the cyclone classifier. On the other hand if an excess of pulp is supplied to tank 22, a safe maximum level is maintained by overflow weir 30. In one successfully working system the control tank operating surface level at 39 is disposed in the plane of the overflow level 30 in the sump. As long as there is any Water in control tank 33 the sump level will be between the line 40 and 41, the line 41 being the level of the botttom of the control tank, but of course proper operation of the system requires that at all times the control tank liquid surface level be maintained at or near the overflow level at 38.

If the pulp density is undesirably high, water may be added to the sump by means of the pipe shown in broken line at 42, but this does not aifect operation of my control system, and is not necessary to proper operation thereof.

What is claimed is:

1. In a pulp-sizing and classifying circuit including means for supplying a water-slurried pulp to a sump tank and also including a pump for transferring the pulp from the sump tank to a cyclone classifier, means for maintaining a constant pulp level in the sump tank comprising a control tank laterally adjacent to said sump tank, a pipe communicating at one end with said sump at an intermediate height thereon and at the other end with the bottom of said control tank, a first overflow outlet near the top of said control tank, a second overflow outlet near the top of said sump tank, said two outlets being at approximately the same horizontal level, means for supplying sufiicient water to said control tank to maintain the liquid level in said control tank as high as the level of said first outlet, whereby, through the intercommunication of said pipe, to maintain a substantially constant level in said sump tank.

2. Apparatus as defined in claim 1 wherein means is provided for restricting liquid flow through said pipe.

3. In a grinding and classifying circuit for processing comminuted taconite slurry, the circuit including means for supplying the slurry to a sump tank and also including a pump for transferring the slurry from the sump tank to sizing and classifying devices, means for maintaining a constant slurry level in the sump tank comprising a control tank laterally adjacent to said sump tank, an interconnecting pipe opening at one end into said sump tank at an intermediate height thereon and at the other end into said control tank near the bottom of said control tank, a control tank overflow outlet near the top thereof, means for supplying sufficient water to said control tank to produce a continuous overflow at said control tank overflow outlet whereby, by reason of the disposition of said interconnecting pipe, a substantially constant level is maintained in said sump tank.

4. Apparatus as defined in claim 3 wherein means is provided for controlling liquid flow through said pipe.

5. In a hydraulic classification circuit, a sump for receiving an iron-rich slurry from a separator; said sump having overflow means for maintaining a selected level of said slurry; pump means continuously removing said slurry from said sump below said selected level; a control tank; said tank having overflow means for maintaining a level of liquid in said tank substantially at said selected level; means forcefully introducing water into said tank at a rate of flow in excess of the rate of flow of said pump means; and means affording liquid communication between said sump and said tank below said selected level.

References Cited by the Examiner UNITED STATES PATENTS 1,629,182 5/27 Stull 209-211 1,743,966 1/30 Goudard 137-576 2,508,170 5/50 Kaufman 137-571 2,556,771 6/51 Moore 137-576 2,573,389 10/51 Bird 209-500 2,870,908 1/59 Fitch 209-211 FOREIGN PATENTS 1,680 5/09 Great Britain. 627,423 3/46 Great Britain.

HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner. 

5. IN A HYDRAULIC CLASSIFICATION CIRCUIT, A SUMP FOR RECEIVING AN IRON-RICH SLURRY FROM A SEPARATOR; SAID SUMP HAVING OVERFLOW MEANS FOR MAINTAINING A SELECTED LEVEL OF SAID SLURRY; PUMP MEANS CONTINUOUSLY REMOVING SAID SLURRAY FROM SAID SUMP BELOW SAID SELECTED LEVEL; A CONTROL TANK; SAID TANK HAVING OVERFLOW MEANS FOR MAINTAINING A LEVEL OF LIQUID IN SAID TANK SUBSTANTIALLY AT SAID SELECTED LEVEL; MEANS FORCEFULLY INTRODUCING WATER INTO SAID TANK AT A RATE OF FLOW IN EXCESS OF THE RATE OF FLOW OF SAID PUMP MEANS; AND MEANS AFFORDING LIQUID COMMUNICTION BETWEEN SAID SUMP AND SAID TANK BELOW SAID SELECTED LEVEL. 